This invention relates to offshore tower constructions which include compliant structures; that is, generally speaking, where a platform or well deck above or below the surface of the water is connected with a sea floor module or base by compliant members placed under tension and lateral deflection of an upper buoyancy module occurs in response to wave, winds, and currents.
In one prior proposed compliant tower structure, a main structural central column was provided which rose from the sea floor and was attached at its top end below the surface of the water to a main buoy which held the column upright under constant tension. Running parallel to the central column and connected thereto by a series of guide means were a plurality of peripheral conductors for well fluids, each connected at its top end to a peripheral buoy which supported the weight of the peripheral conductor to prevent the conductor from entering a compression mode. Wellheads and Christmas wire connected to the top end of the conductors which were used to control the well fluid flow from the sea floor. Fluid is then transmitted to plurality of flexible risers which were attached to the top of the main buoy which was located a distance below the surface of the water, the flexible risers extending to a surface vessel. The central column and the peripheral conductors running parallel thereto and connected by guide means were substantially compliant throughout the length of the conductors and column.
Another prior proposed compliant tower included a truss type construction in which legs of the truss were connected to the sea floor and in which the upper portion of the truss enclosed buoyant tanks. When the truss type tower is subjected to flexing due to ocean current movements, the horizontal and diagonal members of the truss are subjected to high stress concentrations which may result in fatigue failures under extended use.